There are known drop on demand ink jet printer systems in which a print head carriage assembly, which supports a print head, traverses the print head across the width of a print medium in line printing operation. Between lines, the print receiving medium is advanced to prepare for the next line printing sequence. One well known approach is to construct the print head as a unitary, disposable print cartridge which contains an ink supply, drop generating structures, and electrical connections adapted for electrically coupling the print head to the printer which provides drop generating energy in response to print information signals generated by the ink jet printer.
Heretofore, prior art ink jet printers have typically controlled up to five degrees of freedom of the position of the print head with respect to the carriage. Prior art designs have employed various combinations of pad to pad, pin and slot, and knife edge to detent surface alignment schemes. See for example U.S. Pat. No. 4,736,213 issued Apr. 5, 1988, where a cartridge having two alignment pins and a detent surface cooperates with a carriage having two slots and a knife edge to align the cartridge to the carriage. Some of the prior art schemes result in over constraining the cartridge in one or more degrees of freedom, thereby introducing strain and possible distortion of the cartridge, whereas other schemes as noted above underconstrain the cartridge introducing unreliability in the carriage to cartridge interface in one or more degrees of freedom. As the number of ink jets and hence the number of electrical connections to the print head has grown in recent years, it has become increasingly important to precisely locate and exactly constrain the print head with respect to the cartridge. The term exactly constrain as employed herein means to fix each of the three directions x, y and z, and each of the three possible rotations about these directions (all six possible degrees of freedom) without overconstraining any one of the degrees of freedom, thereby avoiding induced stress at the interface. Furthermore, it is desirable to make the ink jet apparatus as small as possible to be portable. Since pads or location planes occurring on adjacent mounting surfaces require considerable area, it is desirable to avoid the use of pad to pad location features.